Polymer particles having good monodispersibility and a nano-sized diameter are drawing much attention and being studied hard, due to various industrial applications in nanomaterials field demanding to be ‘smaller’, ‘smarter’ and ‘faster’. According to the application fields of the nanoparticles, such particles may be used in very industrially important, high value-added materials, such as organic pigments for paints, color balls, a toner, a filler for chromatography, a diagnosis reagent, a chemical/biological sensor, microelectronics, a photonic crystal, a drug delivery material, and the like.
One of the preparation methods of such monodisperse polymer fine particles is emulsion polymerization. Emulsion polymerization which is a method of using a water-soluble, hydrophilic polymerization initiator in a water-insoluble monomer emulsified in water with an emulsifier, is easy to remove polymerization heat, has low viscosity of the emulsion, and has a high molecular weight of the polymer, since the reaction occurs in water. However, the emulsion is easily contaminated with the emulsifier, and it is costly to remove it.
As a prior art to overcome this problem, a polymerization method without an emulsifier, which is called, soap-free emulsion polymerization, is suggested. Soap-free emulsion polymerization which is a method of using a monomer and an ionic hydrophilic initiator or an ionic comonomer without adding an emulsifier, that is, a surfactant, has particularly good monodispersibility of the emulsion. As the mechanism of the method, there is a theory that a polymer adsorbs to a particle nucleus. According to the mechanism, a particle growth process depends on a deposition rate of polymer materials in a bulk; and if a hydrophilic initiator has high concentration, polymer materials in the bulk are increased, and larger particles are synthesized. However, the method has limitations such as a low reaction rate, and using only hydrophobic monomers.